1. Field of the Invention
The present invention relates to a concrete finishing power trowel.
2. Description of the Related Art
Such a power trowel is used predominantly for finishing concrete surfaces, in particular floors, as long as the concrete has not yet hardened. In practice, in addition to manually guided power trowels, ride-on power trowels have proved useful, in which an operator can sit on the device itself and drive it over the concrete that is to be smoothed. In addition to the increased comfort, this makes it possible to avoid leaving footprints on the still-soft concrete surface. Also, in a riding power trowel the weight of the operator sitting on the device provides additional support for its smoothing function.
A power trowel is standardly made up of a frame in which a drive mechanism is housed. The drive drives a rotor, or, in the case of riding power trowels, at least two rotors, each rotor having a drive shaft that is driven by the drive; rotor blades are attached to each drive shaft. The rotor blades extend essentially horizontally, so that the device as a whole sits with the rotor blades on the concrete surface that is to be smoothed. The rotor blades are set into rotation by the drive, and sweep over the surface that is to be smoothed. Because the pitch angle of the rotor blades relative to the drive shaft that bears them can be set, it is possible to achieve a differential pressure effect. Thus, the operator can first cause the rotor blades to sweep over the fresh concrete surface with a relatively flat attack angle and low rotational speed, whereas shortly before the end of the hardening process a higher local pressure, with a significantly steeper attack angle, can be applied to the surface in order to polish it. The setting of the attack angle of the individual rotor blades takes place with the aid of a known blade adjustment device, with which the operator can influence the setting of the rotor blade e.g. via a setting crank.
FIG. 1 shows such a power trowel, as is also known from U.S. Pat. No. 6,368,016 B1. This is a riding power trowel, shown in a schematic perspective view.
On a frame designated 1 as a whole, a seat 2 is situated on which an operator or driver can be seated. Under seat 2 there is situated a drive (not shown), e.g. an internal combustion engine, to which fuel can be supplied via a filling connector 3.
Underneath frame 1, two rotors 4, 5 can be seen. Rotors 4, 5 each have a drive shaft 6 and a plurality of blades 7 (in FIG. 1, each rotor has four blades). Rotors 4, 5 are driven by the drive so as to rotate in opposite directions.
Around rotors 4, 5, a safety cage 8 made up of a plurality of bearing and plate elements is situated in order to prevent accidental intervention in the rotor area, or to prevent driving over the feet of a person standing near the power trowel.
The various possibilities for setting the attack angle of blades 7 are described in U.S. Pat. No. 6,368,016 B1, so that description in more detail is not necessary here.
As is shown, blades 7 are moved rotationally with drive shaft 6 that bears them, so that blades 7 execute a circular movement relative both to drive shaft 6 and also to the surface (concrete surface) that is to be compacted.
In the corners of rooms, there is the problem that blades 7 cannot penetrate all the way into the corner, but rather leave a large area unsmoothed. This area must then be post-processed by hand, which can result in poorer quality of the surface smoothness, and in general entails an increased operating expense.